Earthquake Hazard Assessment of Peninsular India

Neelima Satyam, D1, Pradeep Kumar, Ramancharla1 and Madhav, M R2

1Earthquake Engineering Research Centre, International Institute of Information Technology Hyderabad, Gachibowli,

Hyderabad-32, e-mail: neelima.satyam@iiit.ac.in 2Professor Emeritus, JNT Univ., Hyderabad, India; madhavmr@gmail.com

ABSTRACT

This paper presents the detailed seismic hazard assessment of the peninsular India (lat. 8°-28°N and long. 67.5°-90°E) which is

considered to be seismically most stable landmasses of the Indian plate. Past seismic history in this region (Koyna, 10

December 1967; Bhadrachalam, 13 April 1969; Broach, 23 March 1970; Hyderabad, 30 June 1983; Latur, 30 September 1993;

Jabalpur, 22 May 1997; Bhuj, 26 January 2001 etc) clearly shows that the seismicity of the area is varying. There were more

than five damaging earthquakes with magnitudes greater than Mw 6.0 have occurred in this region, stressing the importance

of

detailed seismic hazard assessment for the region. For India, Bhatia et al. (1999) published a probabilistic seismic hazard map

based on several well identified and prominent source zones in the country. An attempt has been made in this paper to study the

present seismic status of this region incorporating the seismicity, tectonic and geological characteristics and using the collected

earthquake data Peak Ground Acceleration was estimated using the attenuation relation developed by Iyengar and Raghukanth

(2004). Estimated PGA values were used to compute the deviation with respect to assigned PGA values for various regions

provided in Indian Standard code IS 1893:2002. The results show that, the estimated PGA in many areas of the Peninsular India

is more than the specified value in the current seismic macrozonation map of the country. This provides an important basis for

attempting the detailed microzonation of an area within the Penisular India.

Keywords: Seismic hazard, Peak ground acceleration (PGA), Peninsular India, Seismic Zonation

1 INTRODUCTION

India has experienced several major earthquakes in the past

few decades and according to IS 1893: 2002, around 60%

(Zone V= 12%, Zone IV=18%, Zone III = 26% and Zone II

44%) of its landmass is seismically vulnerable. Especially, in

the last two decades, India has witnessed several moderate

earthquakes (Bihar-Nepal border (M6.4) in 1988, Uttarkashi,

Uttaranchal (M6.6) in 1991, Latur, Maharashtra (M6.3) in

1993, Jabalpur, Madhya Pradesh (M6.0) in 1997, Chamoli,

Uttaranchal (M6.8) in 1999, Bhuj, Gujarat (M6.9) in 2001 and

Muzafarrabad,Kashmir (M7.6) in 2005) causing over one

lakh casualties due to collapse of structures. However the

Peninsular region of the country (lat. 8°-28°N and long.

67.5°-90°E) was predominantly considered to be seismically

stable. Figure 1 shows the seismicity of the peninsular India

for a period of around 100 years from 1900 to 2000. From

this, it is apparent that there is a noticeable increment in the

number of earthquakes over a period of time, especially after

1950. Most of the earthquakes occurred in peninsular India

were concentrated near Rann of Kutch. To reduce the damage

due to an earthquake, complete understanding of the seismic

hazard of the region is very important. The study of

destructive earthquake effects in India was started by

Geological Survey of India (Oldham 1899). Later, the Bureau

of Indian Standards (BIS) which is the official agency for

publishing seismic hazard maps and codes in our country,

prepared seismic hazard map consisting of six zones in 1962.

This division was based upon the Maximum Mercalli

Intensities (MMI). In this map, peninsular India is shown as

stable and aseismic region. The third map was published in

1966 dividing India into 7 seismic zones from zone 0 to zone

VI. This map also used geological information of earthquake

activity and tectonic maps that delineated fault system. Some

portion of peninsular India was upgraded from zone 0 to zone

I. The next revision of the seismic hazard map was in 1970

after Koyna earthquake (M 6.5). This map divided India into

5 seismic zones from zone I to zone V based upon

Comprehensive Intensity Scale (CIS–64) historically

observed or expected in those zones. Concept of zone 0 was

abolished in support to the fact that there is no region in India

with probability of an earthquake equal to zero. For the first

time a seismic hazard map was based upon Comprehensive

Intensity Scale (CIS-64). Again in 1984 major revision took

place with 5 seismic zones. In this revision, irrational shape is

assigned to some higher zones because attenuation cannot be

so small. After Latur earthquake in 1993 and Jabalpur

earthquake in 1997, the researchers showed interest towards

comprehensive study on the seismic hazard map of the

country. Fifth revision of IS 1893:2002 took place

immediately after the devastating Bhuj earthquake in 2001. In

this revision, only 4 zones were adopted viz., zone II, III, IV

and V (Fig: 2d). Zone II being low damage risk zone and Zone

V being high damage risk zone. Also, most of peninsular

region is upgraded to zone II and III. Zone I is completely

discarded in this revision. In this regard, large portion of

Peninsular India was upgraded. In addition to this, Khattri et

al. (1987) produced a probabilistic seismic hazard map in

units of g, for 10 per cent probability of exceedence over the

next 50 yr period. The study of Bhatia et al. (1999) under the

Global Seismic Hazard Assessment Programme (GSHAP) is

based on a probabilistic approach. The computational

schemes involved in both the studies are delineation of

seismic source zones and their characterizations; selection of

an appropriate ground motion attenuation relation with source

site distance and a predictive model of seismic hazard. In the

above studies, the attenuation relation produced for the

United States (Algermissen and Perkins 1976; Joyner and

Boore 1981) has been applied. A comparison of the

attenuation relationships for many different areas shows that

0

20

40

60

80

100

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Frequency of Earthquakes (Mw>3)

the attenuation laws may differ very significantly from one

region to another due to the tectonic, seismic, geological and

geotechnical differences. A study done by Khatri eta al.

1984 and Bhatia et al 1999 provides only a macroscopic

picture of seismic hazard with out incorporating the

earthquake recurrence data.

Figure 1 Frequency of earthquakes from the year

1990-2000 in Peninsular India

A regional seismic hazard assessment in terms of earthquake

magnitude and annual exceedence probability has been

presented by Kishore and Ravi Sinha (2008). The main aim of

this article is to estimate the actual existing seismic hazard

associated with the entire Peninsular region which will be

useful for attempting detailed regional seismic microzonation

studies. Because underestimation of the seismic hazard leads

to the questionable safely and overestimate leads to

uneconomical design. A detailed study was carried out using

the data of several earthquakes occurred with in the Indian

peninsular region for estimating the Peak Ground

Acceleration using Iyengar and Raghukanth (2004)

attenuation relationship and the estimated PGA values were

compared with the values given in IS 1893-2002.

2 GEOLOGICAL AND TECTONIC DETAILS OF INDIAN

PENINSULA

The Peninsular India consists of gneiss and schists which are

very old rock formations. The Precambrian rocks of India

have been classified into two systems, the Dharwar system

and the Archaean system. The rocks of the Dharwar system

are mainly sedimentary in origin, and occur in narrow

elongated synclines resting on the gneisses found in Mysore

and the Aravalis of Rajputana. These rocks highly enriched

with mineral deposits.The Peninsular Shield of India is made

up of three main regions the Aravalli, the Dharwar and the

Singhbhum which are separated by Proterozoic rifts and

mobile belts. The major prominent rifts that separate the

southern and northern blocks of the shield are the Narmada

Son Lineament (NSL) and the Tapti Lineament (TL), together

called the Son-Narmada Tapti lineament. The other rift basins

are the Kutch, Cambay, Godavari, Cuddapah etc. (Yedekar et

al. 1990). Rifting zones like Narmada and Rann of Kutch in

this Peninsular region had experienced severe earthquakes

like Anjar earthquake 1958, Jabalpur earthquake 1997, Bhuj

2001 etc in the past. Seeber et al. (1999) proposed nine

seismic zones based on geology, tectonic features and

observed seismicity. Naqvi et al 1974 classified them broadly

into cratonic and paleorifting zones. Cratons are highly stable

interior portion of the Peninsular shield like Northern, Eastern

and Southern cartons. Paleorifting regions containing large

faults and has experienced deformations in their most active

phase, which are narmada, Cambay and Mahanadi grabens.

The detailed geology and the tectonics of the region were

presented by Valdiya (1973), Naqvi and Ragers (1987) and

many others. Figure 2a and 2b shows the detailed geological

and tectonic map of the Peninsular India.

3 SEISMIC CHARACTERISTICS OF PENINSULAR

INDIA

The entire Indian subcontinent is composed of three major

plates viz., Indian plate, Eurasian plate and Australian plate

and many minor plates like Burma plate, Sunda plate etc.

Distinct physical and kinematic properties of these plates lead

to a diversified seismicity from one region to another in

Indian subcontinent. On the basis of historic seismic trend,

Indian shield can be easily classified as seismically active at

the Himalayan, Karakoram, and Tibetan plateau belt

stretching approximately 2500 km line and somewhat

seismically moderate in the peninsular shield. Various regions

were identified and classified on the basis of their seismic

activity. Since these seismic activities are random in nature,

classification merely on the basis of major seismic activities is

always been a topic of debate among the researchers.

Seismicity trend of India classifies it as a highly varied

country in terms of seismic activities. It is very clear that there

is a broad variation in seismic hazard levels in terms of the

intensity of ground motion and the frequency of occurrence.

These variations divided India into different zones with

respect to the severity of expected ground motion. Figure 2c

shows the observed seismicity of the peninsular region. In this

paper a detailed seismic hazard assessment of the peninsular

India has been carried out. This can be further used for doing

detailed seismic microzonation studies.

4 SEISMIC HAZARD ASSESSMENT

Seismic databases and earthquake catalogues are very crucial

and important parameter in any seismic hazard analysis and

microzonation studies. For the considered range of latitudes

and longitudes, earthquake data was collected for peninsular

region (PI) region from Seismotectonic Atlas of India and its

environs (GSI, 2001) and a working data table has been

prepared. Data was collected from a uniform source in order

to maintain the uniformity in computation. Then all the

magnitudes values were converted to uniform moment

magnitude values using the formula given by Scordilis (2006).

This formula makes use of mbw and Msw. In case of both mb

and Ms values available for an event in a record, the

conversion relations proposed by Scordilis (2006) has been

used and then estimated the weighted average of the

converted magnitudes using the conversion formula. Mw

values computed based upon mb and Ms as mbw and Msw

respectively corresponds the final magnitude (Mw) was

computed using Eqn. 1.

(a) (b)

(c) (d)

Figure 2 (a) Geological details of Peninsular India; (b) tectonic features of Indian Peninsula; (c)

Seismicity details of PI and (d) Seismic zonation map of India (IS 1893: 2002)

21

21

11

σσ

σσ

+

+

=

Swbw

W

Mm

M (1)

Where corresponding values of 1σ and 2σ are as

shown below:

For 3≤ Ms ≤ 6.1, 2σ = 0.17

For 6.2 ≤Ms ≤ 8.2, 2σ = 0.20

For 3.5 ≤ mb ≤ 6.2, 1σ = 0.29

Moreover at the places where only mb or Ms values were

available, Mw was computed directly on the basis of

whatever source value (either mb or Mw).

Msw =0.67(±0.005) Ms + 2.07(±0.03) (2)

3.0≤Ms≤ 6.1,R2 =0.77, σ2 = 0.17,n = 23,921

Msw =0.99(±0.02) Ms + 0.08(±0.13) (3)

6.2≤Ms≤ 8.2, R2 =0.81, σ2 = 0.20, n = 2,382

mbw =0.85(±0.04)mb + 1.03(±0.23) (4)

3.5≤ mb≤6.2, R2 =0.53, σ1 = 0.29,n= 9,784

The Peak ground acceleration (PGA) at any location

can be estimated using empirical attenuation

relationships proposed for different seismic regions

(Interplate, Intraplate, and Subduction). Every

attenuation relationship is different from another in

terms of applicability that is limited depending upon

certain factors like the type of soil (Hard/rock,

medium or soft), type of region (Interplate, Intraplate

or Subduction), type of fault (Normal, reverse,

strike-slip) and so on. Since the actual values of all

these parameters were not present, empirical

relationships and few logical assumptions were made

in the computation of PGA. Iyengar and Raghukanth

(2004) proposed the attenuation relationship to

compute the PGA of PI region as shown in Eqn 5

below.

εlnln)6()6(ln 4

2

321 +−−−+−+= RcRMcMccy (5)

Where y, M and R refer to PGA, moment magnitude

and hypocentral distance respectively.

A computer code has been developed to estimate the

PGA(y) for different values of Mw and R

corresponding to earthquakes belonging to different

classifications within Peninsular region. The code

was developed in such a manner that by reading the

latitude and longitude of the earthquake it assesses the

region (koyna-warna, western central or south region)

in which this earthquake has occurred and suitable

constants will be used to compute the PGA value. A

total of around 250 earthquake records occurred PI

region were considered in this study. For estimating

the deviations of PGA assigned for various zones in

the Peninsular region, collected earthquake data was

used and Peak Ground Acceleration was estimated

using the Iyengar and Raghukanth (2004) attenuation

relation. Percentage deviation was computed

considering the Eqn. 6 as shown below. Estimated

PGA values were used to compute the deviation with

respect to assigned PGA values for various regions

according to IS 1893:2002.

100(%) xPGA

PGAPGADeviation

computed

computedzone −= (6)

Table 1 shows the details of few records showing the

event date, latitude and longitude, assumed

hypocentral radius, computed moment magnitude,

PGA using attenuation relationship, zone details, code

based PGA and percentage deviation calculated for

zone II, III and V.

5 RESULT AND CONCLUSIONS

In this study the major concern was to estimate the actual

earthquake hazard associated with the Peninsular India

which is considered to be more stable landmass in the

Indian plate. This region which is an intraplate region

experienced several devastating earthquakes in the past.

The seismic data was collected for PI region from a

uniform source i.e., Seismotectonic Atlas of India and its

environs (GSI, 2001) and a working data table has been

prepared. A computer code was developed to estimate

the Peak ground acceleration (PGA) using empirical

attenuation relationships proposed for Peninsular India

by Iyengar and Raghukanth (2004). The average

percentage deviations in the PGA values were estimated.

From the analysis, the percentage deviation obtained

was classified into 7 different levels ie., less than 0%,

0-20%, 20-40%, 40-60%, 60-80% 80-100% and greater

than 100%. These percentage deviations were then

studied with respect to different zones in which the

region under study is classified. The negative values of

deviation indicates that, the computed PGA to be more

as compared to zone based PGA value defined as per

code and hence indicating the underestimated values of

PGA

Figure 3 Average Percentage deviation of PGA values at different Hypocentral Radius (a): 5km; (b):10km;

(c):15km and (d):20km

(a) (b)

(c) (d)

Table 1 (a) Details of PGA estimated for different seismic events and corresponding Percentage PGA

deviation for PI in Zone II

Date Latitude Longitude Hypocentral

Radius (km)

Moment

Magnitude

(Mw)

Estimated

PGA (g)

Zone

basis

PGA

Percentage

Deviation

09/29/1993 18.10 76.64 5 5.2 0.505 0.1 -80.21

09/29/1993 18.08 76.47 5 6.2 1.3400 0.1 -92.53

06/21/1995 21.76 85.28 5 5 0.3917 0.1 -74.47

06/21/1995 21.76 85.29 5 5 0.392 0.1 -74.47

12/14/1995 18.11 76.53 5 4.7 0.294 0.1 -66.04

05/22/1998 21.62 84.45 5 4.4 0.198 0.1 -49.48

06/19/2000 18.17 76.62 5 4.7 0.294 0.1 -66.04

10/01/1993 18.11 76.44 5 4.8 0.329 0.1 -69.61

10/08/1993 17.97 76.41 5 4.9 0.367 0.1 -72.76

11/12/1993 18.09 76.53 5 4.9 0.367 0.1 -72.76

05/21/1997 23.09 80.08 10 5.9 0.4779 0.1 -79.07

09/29/1993 18.10 76.64 10 5.2 0.242 0.1 -58.70

01/19/1986 21.01 85.22 10 4.8 0.152 0.1 -34.20

09/29/1993 18.10 76.64 10 5.2 0.242 0.1 -58.70

09/30/1993 18.23 76.64 10 4.8 0.157 0.1 -36.54

10/01/1993 18.10 76.44 10 4.8 0.157 0.1 -36.54

10/8/1993 17.96 76.41 10 4.9 0.175 0.1 -43.12

06/30/1983 17.92 78.54 10 5.2 0.263 0.1 -61.98

06/21/1995 21.76 85.28 10 5 0.1897 0.1 -47.28

09/29/1993 18.08 76.47 10 6.2 0.6418 0.1 -84.41

09/29/1993 18.10 76.64 15 5.2 0.1546 0.1 -35.32

09/29/1993 18.08 76.47 15 6.2 0.4098 0.1 -75.60

06/30/1983 17.92 78.54 15 5.2 0.1723 0.1 -41.96

06/21/1995 21.76 85.28 15 5 0.1224 0.1 -18.35

10/20/2003 23.88 86.32 15 4.4 0.0618 0.1 61.57

12/14/1995 18.11 76.53 15 4.7 0.0901 0.1 11.018

05/22/1998 21.61 84.44 15 4.4 0.0618 0.1 61.571

06/19/2000 18.16 76.62 15 4.7 0.0900 0.1 11.018

05/21/1997 23.09 80.08 15 5.9 0.3085 0.1 -67.59

01/19/1986 21.01 85.22 20 4.8 0.0712 0.1 40.28

03/17/1986 22.86 85.15 20 4.7 0.0636 0.1 57.067

09/29/1993 18.10 76.64 20 5.2 0.1111 0.1 -9.982

09/29/1993 18.08 76.47 20 6.2 0.2944 0.1 -66.041

09/30/1993 18.23 76.64 20 4.8 0.0723 0.1 38.308

09/30/1993 18.08 76.49 20 4.9 0.0806 0.1 23.964

10/01/1993 18.11 76.44 20 4.8 0.0723 0.1 38.308

10/08/1993 17.96 76.41 20 4.9 0.0806 0.1 23.964

05/22/1998 21.61 84.44 20 4.4 0.0449 0.1 122.43

06/19/2000 18.16 76.619 20 4.7 0.0647 0.1 54.528

Date Latitude Longitude Hypocentral

Radius (km)

Moment

Magnitude

(Mw)

Estimated

PGA (g)

Zone

basis

PGA

Percentage

Deviation

09/29/1993 18.10 76.64 5 5.2 0.505 0.1 -80.21

09/29/1993 18.08 76.47 5 6.2 1.3400 0.1 -92.53

06/21/1995 21.76 85.28 5 5 0.3917 0.1 -74.47

06/21/1995 21.76 85.29 5 5 0.392 0.1 -74.47

12/14/1995 18.11 76.53 5 4.7 0.294 0.1 -66.04

05/22/1998 21.62 84.45 5 4.4 0.198 0.1 -49.48

06/19/2000 18.17 76.62 5 4.7 0.294 0.1 -66.04

10/01/1993 18.11 76.44 5 4.8 0.329 0.1 -69.61

10/08/1993 17.97 76.41 5 4.9 0.367 0.1 -72.76

11/12/1993 18.09 76.53 5 4.9 0.367 0.1 -72.76

05/21/1997 23.09 80.08 10 5.9 0.4779 0.1 -79.07

09/29/1993 18.10 76.64 10 5.2 0.242 0.1 -58.70

01/19/1986 21.01 85.22 10 4.8 0.152 0.1 -34.20

09/29/1993 18.10 76.64 10 5.2 0.242 0.1 -58.70

09/30/1993 18.23 76.64 10 4.8 0.157 0.1 -36.54

10/01/1993 18.10 76.44 10 4.8 0.157 0.1 -36.54

10/8/1993 17.96 76.41 10 4.9 0.175 0.1 -43.12

06/30/1983 17.92 78.54 10 5.2 0.263 0.1 -61.98

06/21/1995 21.76 85.28 10 5 0.1897 0.1 -47.28

09/29/1993 18.08 76.47 10 6.2 0.6418 0.1 -84.41

09/29/1993 18.10 76.64 15 5.2 0.1546 0.1 -35.32

09/29/1993 18.08 76.47 15 6.2 0.4098 0.1 -75.60

06/30/1983 17.92 78.54 15 5.2 0.1723 0.1 -41.96

06/21/1995 21.76 85.28 15 5 0.1224 0.1 -18.35

10/20/2003 23.88 86.32 15 4.4 0.0618 0.1 61.57

12/14/1995 18.11 76.53 15 4.7 0.0901 0.1 11.018

05/22/1998 21.61 84.44 15 4.4 0.0618 0.1 61.571

06/19/2000 18.16 76.62 15 4.7 0.0900 0.1 11.018

05/21/1997 23.09 80.08 15 5.9 0.3085 0.1 -67.59

01/19/1986 21.01 85.22 20 4.8 0.0712 0.1 40.28

03/17/1986 22.86 85.15 20 4.7 0.0636 0.1 57.067

09/29/1993 18.10 76.64 20 5.2 0.1111 0.1 -9.982

09/29/1993 18.08 76.47 20 6.2 0.2944 0.1 -66.041

09/30/1993 18.23 76.64 20 4.8 0.0723 0.1 38.308

09/30/1993 18.08 76.49 20 4.9 0.0806 0.1 23.964

10/01/1993 18.11 76.44 20 4.8 0.0723 0.1 38.308

10/08/1993 17.96 76.41 20 4.9 0.0806 0.1 23.964

05/22/1998 21.61 84.44 20 4.4 0.0449 0.1 122.43

06/19/2000 18.16 76.619 20 4.7 0.0647 0.1 54.528

Table 1 (b) Details of PGA estimated for different seismic events and corresponding Percentage PGA

deviation for PI in Zone III

Date Latitude Longitude Hypocentral

Radius (km)

Moment

Magnitude

(Mw)

Estimated

PGA (g)

Zone

basis

PGA

Percentage

Deviation

04/18/1987 22.52 79.24 5 5.1 0.436 0.16 -63.36

03/27/1995 21.66 84.59 5 4.8 0.314 0.16 -49.02

05/24/1995 16.43 79.64 5 4.9 0.391 0.16 -59.07

01/10/1996 22.20 77.61 5 4.4 0.198 0.16 -19.17

08/04/1996 16.64 80.02 5 4.5 0.252 0.16 -36.56

09/12/2000 21.81 72.42 5 4.3 0.176 0.16 -8.96

10/10/2000 23.01 82.78 5 4.5 0.223 0.16 -28.13

10/16/2000 23.27 80.29 5 4.8 0.314 0.16 -49.02

03/10/2003 21.40 77.21 5 4.3 0.176 0.16 -8.96

07/27/2003 21.88 74.34 5 4.2 0.156 0.16 2.96

04/18/1987 22.52 79.24 10 5.1 0.2114 0.16 -24.33

08/24/1993 20.69 71.44 10 5.2 0.2353 0.16 -32.02

01/10/1996 22.20 77.60 10 4.4 0.0958 0.16 66.91

08/4/1996 16.64 80.02 10 4.5 0.1239 0.16 29.12

11/17/1996 21.40 73.06 10 4.4 0.0958 0.16 66.91

01/23/1997 17.14 76.69 10 5 0.1958 0.16 -18.32

06/4/1997 23.08 80.04 10 4.3 0.0851 0.16 88.00

03/9/1998 22.53 78.18 10 4.5 0.1078 0.16 48.41

03/29/1998 22.51 79.25 10 4.3 0.0851 0.16 88.00

12/31/1993 21.11 72.71 10 4.2 0.0754 0.16 112.06

08/24/1993 20.69 71.44 15 5.2 0.1519 0.16 5.2816

10/26/1983 23.75 85.67 15 4.3 0.0549 0.16 191.16

04/18/1987 22.52 79.24 15 5.1 0.1365 0.16 17.18

12/3/1987 15.51 80.21 15 4.9 0.1258 0.16 27.16

08/24/1993 20.69 71.44 15 5.2 0.1519 0.16 5.281

12/31/1993 21.11 72.71 15 4.2 0.0487 0.16 228.43

03/27/1995 21.66 84.58 15 4.8 0.0981 0.16 63.03

05/24/1995 16.42 79.63 15 4.9 0.1258 0.16 27.169

01/10/1996 22.20 77.60 15 4.4 0.0618 0.16 158.51

10/26/1983 23.75 85.67 20 4.3 0.0399 0.16 300.85

04/18/1987 22.52 79.24 20 5.1 0.0991 0.16 61.323

12/03/1987 15.51 80.21 20 4.9 0.0927 0.16 72.55

08/24/1993 20.69 71.44 20 5.2 0.1103 0.16 44.94

12/31/1993 21.11 72.71 20 4.2 0.0353 0.16 352.15

03/27/1995 21.66 84.58 20 4.8 0.0712 0.16 124.44

05/24/1995 16.42 79.63 20 4.9 0.0927 0.16 72.553

01/10/1996 22.20 77.60 20 4.4 0.0449 0.16 255.89

08/04/1996 16.64 80.024 20 4.5 0.0598 0.16 167.44

11/17/1996 21.402 73.060 20 4.4 0.0449 0.16 255.89

Table 1 (c) Details of PGA estimated for different seismic events and corresponding Percentage PGA

deviation for PI in Zone V

Date Latitude Longitude Hypocentral

Radius (km)

Moment

Magnitude

(Mw)

Estimated

PGA (g)

Zone

basis

PGA

Percentage

Deviation

1/26/2001 23.506 70.517 5 5.1 0.4366 0.36 -17.560

1/26/2001 23.424 70.847 5 5.2 0.4860 0.36 -25.934

1/26/2001 23.348 70.441 5 5.3 0.5402 0.36 -33.358

1/26/2001 23.431 70.216 5 5.3 0.5402 0.36 -33.358

1/26/2001 23.246 69.947 5 5.3 0.5402 0.36 -33.358

1/26/2001 23.522 70.076 5 5.5 0.6643 0.36 -45.809

1/26/2001 23.425 70.096 5 5.6 0.7350 0.36 -51.024

1/26/2001 23.421 70.119 5 5.9 0.9869 0.36 -63.525

1/26/2001 23.442 70.31 5 7.9 5.0082 0.36 -92.811

1/26/2001 23.369 70.563 5 5 0.3917 0.36 -8.1040

1/26/2001 23.369 70.563 10 5 0.1897 0.36 89.768

8/1/2001 23.685 70.652 10 4.4 0.095 0.36 275.56

8/3/2001 23.591 70.269 10 4.6 0.121 0.36 197.366

8/4/2001 23.49 70.455 10 4.4 0.095 0.36 275.562

8/8/2001 23.53 70.444 10 4.2 0.075 0.36 377.137

8/24/2001 23.213 70.729 10 4.6 0.121 0.36 197.366

9/20/2001 23.596 70.529 10 4.6 0.121 0.36 197.366

9/21/2001 23.496 70.179 10 4.3 0.085 0.36 323.000

10/3/2001 23.278 70.299 10 4.4 0.0958 0.36 275.562

10/21/2001 23.417 70.565 10 4 0.0590 0.36 509.783

10/31/2001 23.684 70.138 15 4.8 0.0981 0.36 266.826

11/17/2001 23.673 70.181 15 4.6 0.0781 0.36 360.553

11/24/2001 23.639 70.588 15 4.8 0.0981 0.36 266.826

12/1/2001 23.394 70.284 15 4.5 0.0696 0.36 417.194

12/12/2001 23.693 70.498 15 4.4 0.0618 0.36 481.661

12/21/2001 23.686 70.181 15 4.8 0.0981 0.36 266.826

1/9/2002 23.564 70.411 15 4.6 0.0781 0.36 360.553

1/18/2002 23.568 70.193 15 4.6 0.0781 0.36 360.553

2/16/2002 23.791 70.84 15 4 0.0381 0.36 844.418

11/17/2001 23.673 70.181 20 4.6 0.0567 0.36 534.039

11/24/2001 23.639 70.588 20 4.8 0.0712 0.36 405.006

12/1/2001 23.394 70.284 20 4.5 0.0505 0.36 612.016

12/12/2001 23.693 70.498 20 4.4 0.0449 0.36 700.76

12/21/2001 23.686 70.181 20 4.8 0.0712 0.36 405.00

1/9/2002 23.564 70.411 20 4.6 0.0567 0.36 534.03

1/18/2002 23.568 70.193 20 4.6 0.0567 0.36 534.03

2/16/2002 23.791 70.84 20 4 0.0276 0.36 1200.1

2/20/2002 23.619 70.197 20 4.5 0.0505 0.36 612.01

3/27/2002 23.662 70.169 20 4.5 0.0505 0.36 612.01

in our design code of practice. On the other hand, positive

values of deviation indicate computed PGA is less than zone

based PGA value defined and hence indicating the

overestimated values of PGA in our design code of practice.

Figure 3 shows the average Percentage deviation in PGA

values for different Hypocentral Radius considered in the

study. Contour map and percentage deviation for hypocentral

radius of 5 km as shown in Fig. 3(a) and observed that this

value is too small to consider for deviation calculations

because this 5 km makes epicentral distance too small. It was

also observed that for hypocentral radius of 10 km (Fig: 3b) a

much wider spectrum of percentage deviations was obtained.

This signifies the uneven trend of seismicity in the region and

more rigid definition of PGA for an area with hypocentral

radius equals to 10 km. Moreover for this range of radius most

of the zone II region was qualified as underestimated region.

It means that the PGA value estimated using attenuation

formula was greater than the PGA value proposed by the code.

The overall average deviation for zone II was estimated to be

-28%. Similarly for zone III it is +63%, zone IV it is +182%

and for zone V it is +239%. In the same manner, average %

deviations were estimated for other ranges of hypocentral

radius as well. In case of 15 km (Fig: 3c) and 20 km (Fig: 3d)

all the zones II, III, IV and V were evaluated with all positive

values of average % deviations, indicating overestimated

values of PGA for different zones.

Moreover, overall deviation towards overestimated rate was

observed at higher hypocentral radius. For zone II, III, IV and

V and for hypocentral radius of 15 km, the values were

obtained to be all positive. While for hypocentral radius 20

km these deviations are much higher. These differences in

values clearly indicate that the average deviations are more

towards overestimated scenarios for higher hypocentral radii.

Finally, it is clear

that the PGA values are over estimated in lower seismic

zones especially zone II and III for hypocentral radius

ranging from 10 km to 20 km. For higher values of

hypocentral radius it is found that PGA values of all the

zones are over estimated. In this regard, it is strongly

recommended that serious attention is required for

understanding macro seismotectonics of Indian plate for

arriving at the macro hazard map. For attempting the

detailed seismic microzonation of any area within the

Penisular India this research can provide an important

basis.

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